The goal of this proposal is to study the regulation and interaction of specific molecules of the Serotonrn (5HT) system and the Limbic-Hypothalamic-Pituitary-Adrenal (LHPA) axis in key regions of the rat brain (hippocampus, hypothalamus, and prefrontal cortex); using biochemical and neuroanatomical tools. Dysfunction of the 5HT system and overactivity of the LHPA axis are two of the most replicated biological fmdings in depression. Our overall hypothesis is that the alterations in these two systems are closely linked. Specifically, based on our previous animal and human postmortem studies, we propose the following hypotheses: 1) that glucocorticoids play a central role in the 5HT and corticosteroid receptor dysregulation found in depression and in chronic stress; 2) that failure of an antidepressant to prevent the LHPA overactivity is associated with a failure to reverse these receptor changes; 3) that blocking the effect of glucocorticoids in brain will prevent the receptor abnormalities; and 4) that environmental factors early in life can contribute to LHPA 'dysfunction' and 5HT receptor abnormalities. To answer these hypotheses, on Aims 1 and 2 we will use rats to investigate whether chronic stress causes concomitant changes in brain 5HT, corticosteroid, and CRH receptors. We will also investigate whether antidepressants prevent these changes, and whether circulating corticosteroids have a central role on these stress-induced receptor 'abnormalities'. Aim 3 will investigate whether administration of DHEA, an androgen with antiglucocorticoid properties, or administration of a CR11 receptor antagonist, will reverse and/or prevent these receptor changes. Aim 4 will investigate whether maternal deprivation in rats makes the brain more vulnerable to these receptor changes in adulthood.We will use in situ hybridization, radioimmunocytochemistry, and receptor autoradiography to quantify: 5HT1a and 5HT2a receptors, 5HT transporter, Glucocorticoid and Mineralocorticoid receptors, Corticotropin releasing hormone (CRH), CRH receptors, and CRH binding protein. This proposal brings together molecular/neuroanatomical tools, to increase our knowledge of the link between stress and depression. It is hoped that these series of 'preclinical' animal studies will help increase our understanding of the pathophysiological consequences of chronic stress, will help clarify the role of elevated corticosteroids in depression, and will give us someclues about how to treat, or prevent, the cumulative effect of hypercortisolemia in brain.